Over-centering blade lock

ABSTRACT

An exemplary blade lock for a tiltrotor aircraft to enable and disable a folding degree of freedom and a pitching degree of freedom of a rotor blade assembly includes a link pivotally connected to a lever and a bellcrank, where the link is in a center position when the lever is in a locked position disabling the folding degree of freedom and the lever is secured in the locked position when the link is positioned in an over-center position.

TECHNICAL FIELD

This disclosure relates in general to the field of aircraft, and moreparticularly, to tiltrotor aircraft operable for vertical takeoff andlanding in a helicopter mode and high-speed forward cruising in anairplane flight mode and, in particular, to tiltrotor aircraft operablefor transitions between rotary and non-rotary flight modes.

BACKGROUND

This section provides background information to facilitate a betterunderstanding of the various aspects of the disclosure. It should beunderstood that the statements in this section of this document are tobe read in this light, and not as admissions of prior art.

Fixed-wing aircraft, such as airplanes, are capable of flight usingwings that generate lift responsive to the forward airspeed of theaircraft, which is generated by thrust from one or more jet engines orpropellers. The wings generally have an airfoil cross section thatdeflects air downward as the aircraft moves forward, generating the liftforce to support the aircraft in flight. Fixed-wing aircraft, however,typically require a runway that is hundreds or thousands of feet longfor takeoff and landing.

Unlike fixed-wing aircraft, vertical takeoff and landing (VTOL) aircraftdo not require runways. Instead, VTOL aircraft are capable of takingoff, hovering and landing vertically. One example of a VTOL aircraft isa helicopter which is a rotorcraft having one or more rotors thatprovide lift and thrust to the aircraft. The rotors not only enablehovering and vertical takeoff and landing, but also enable forward,backward and lateral flight. These attributes make helicopters highlyversatile for use in congested, isolated or remote areas. Helicopters,however, typically lack the forward airspeed of fixed-wing aircraft dueto the phenomena of retreating blade stall and advancing bladecompression.

Tiltrotor aircraft attempt to overcome this drawback by utilizingproprotors that can change their plane of rotation based on theoperation being performed. Tiltrotor aircraft typically have a pair ofnacelles mounted near the outboard ends of a fixed wing with eachnacelle housing a propulsion system that provides torque and rotationalenergy to a proprotor. The nacelles are rotatable relative to the fixedwing such that the proprotors have a generally horizontal plane ofrotation providing vertical thrust for takeoff, hovering and landing,much like a conventional helicopter, and a generally vertical plane ofrotation providing forward thrust for cruising in forward flight withthe fixed wing providing lift, much like a conventional propeller drivenairplane. It has been found; however, that forward airspeed inducedproprotor aeroelastic instability is a limiting factor relating to themaximum airspeed of tiltrotor aircraft in forward flight.

SUMMARY

An exemplary blade lock for a tiltrotor aircraft to enable and disable afolding degree of freedom and a pitching degree of freedom of a rotorblade assembly includes a link pivotally connected to a lever and abellcrank, where the link is in a center position when the lever is in alocked position disabling the folding degree of freedom and the lever issecured in the locked position when the link is positioned in anover-center position.

An exemplary tiltrotor aircraft having rotary and non-rotary flightmodes includes a rotor assembly having a gimballing degree of freedomrelative to a mast, the rotor assembly including a plurality of rotorblade assemblies each having a pitching degree of freedom and a foldingdegree of freedom; a gimbal lock positioned about the mast, the gimballock having a disengaged position relative to the rotor assembly,enabling the gimballing degree of freedom, in the rotary flight mode andan engaged position relative to the rotor assembly, disabling thegimballing degree of freedom, in the non-rotary flight mode; a bladestop assembly positioned about the mast, the blade stop assemblyincluding a plurality of arms having a radially contracted orientation,in the rotary flight mode and a radially extended orientation, in thenon-rotary flight mode; a blade lock assembly operably associated witheach rotor blade assembly, each blade lock assembly having a fold lockedposition, disabling the folding degree of freedom and enabling thepitching degree of freedom of the respective rotor blade assembly, inthe rotary flight mode and a pitch locked position, enabling the foldingdegree of freedom and disabling the pitching degree of freedom of therespective rotor blade assembly, in the non-rotary flight mode; and theblade lock assembly comprising a link pivotally connected to a pitchlock and a fold lock, wherein the link is in a center position when thefold lock is in the fold locked position and the fold lock is secured inthe fold locked position when the link is positioned over-centerposition and the pitch lock contacts a hard stop.

An exemplary method for enabling and disabling a folding degree offreedom and a pitching degree of freedom of a rotor blade assembly of atiltrotor aircraft includes rotating a blade lock comprising a pitchlock pivotally connected to a fold lock by a link from a pitch lockedposition to a fold locked position, where in the fold locked positionthe link is located in a center position and rotating the pitch lockinto contact with a hard stop thereby positioning the link in anover-center position.

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofclaimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-1D are schematic illustrations of an exemplary tiltrotoraircraft in various flight modes in accordance with aspects of thedisclosure.

FIGS. 2A-2G are isometric views of an exemplary mechanism fortransitioning a tiltrotor aircraft between rotary and non-rotary flightmodes, in various positions, in accordance with aspects of thedisclosure.

FIGS. 3A-3E are isometric views of an exemplary blade lock assembly of amechanism for transitioning a tiltrotor aircraft between rotary andnon-rotary flight modes, in various positions, in accordance withaspects of the disclosure.

FIGS. 4 and 5 illustrate an exemplary over-centering blade lock in thefold locked position.

FIG. 6 illustrates an exemplary over-centering blade lock in the pitchlocked position.

FIG. 7 illustrates an exemplary hard stop adjustment mechanism.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various illustrative embodiments. Specific examples of components andarrangements are described below to simplify the disclosure. These are,of course, merely examples and are not intended to be limiting. Forexample, a figure may illustrate an exemplary embodiment with multiplefeatures or combinations of features that are not required in one ormore other embodiments and thus a figure may disclose one or moreembodiments that have fewer features or a different combination offeatures than the illustrated embodiment. Embodiments may include somebut not all the features illustrated in a figure and some embodimentsmay combine features illustrated in one figure with features illustratedin another figure. Therefore, combinations of features disclosed in thefollowing detailed description may not be necessary to practice theteachings in the broadest sense and are instead merely to describeparticularly representative examples. In addition, the disclosure mayrepeat reference numerals and/or letters in the various examples. Thisrepetition is for the purpose of simplicity and clarity and does notitself dictate a relationship between the various embodiments and/orconfigurations discussed.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present application, the devices,members, apparatuses, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “inboard,”“outboard,” “above,” “below,” “upper,” “lower,” or other like terms todescribe a spatial relationship between various components or todescribe the spatial orientation of aspects of such components should beunderstood to describe a relative relationship between the components ora spatial orientation of aspects of such components, respectively, asthe device described herein may be oriented in any desired direction. Asused herein, the terms “connect,” “connection,” “connected,” “inconnection with,” and “connecting” may be used to mean in directconnection with or in connection with via one or more elements.Similarly, the terms “couple,” “coupling,” and “coupled” may be used tomean directly coupled or coupled via one or more elements.

Referring to FIGS. 1A-1D in the drawings, a tiltrotor aircraft isschematically illustrated and generally designated 10. Aircraft 10includes a fuselage 12, a wing 14 and a tail assembly 16 includingcontrol surfaces operable for horizontal and/or vertical stabilizationduring forward flight. Located proximate the outboard ends of wing 14are pylon assemblies 18 a, 18 b that are rotatable relative to wing 14between a generally vertical orientation, as best seen in FIG. 1A, and agenerally horizontal orientation, as best seen in FIGS. 1B-1D. Pylonassemblies 18 a, 18 b each house a portion of the drive system that isused to rotate proprotor assemblies 20 a, 20 b, respectively. Eachproprotor assembly 20 a, 20 b includes a plurality of proprotor blades22 that are operable to be rotated, as best seen in FIGS. 1A-1B,operable to be feathered, as best seen in FIG. 1C and operable to befolded, as best seen in FIG. 1D. In the illustrated embodiment,proprotor assembly 20 a is rotated responsive to torque and rotationalenergy provided by engine 24 a and proprotor assembly 20 b is rotatedresponsive to torque and rotational energy provided by engine 24 b.Engines 24 a, 24 b are located proximate an aft portion of fuselage 12.Engines 24 a, 24 b are operable in a turboshaft mode, as best seen inFIGS. 1A-1B and a turbofan mode, as best seen in FIGS. 1C-1D.

FIG. 1A illustrates aircraft 10 in VTOL or helicopter flight mode, inwhich proprotor assemblies 20 a, 20 b are rotating in a substantiallyhorizontal plane to provide a lifting thrust, such that aircraft 10flies much like a conventional helicopter. In this configuration,engines 24 a, 24 b are operable in turboshaft mode wherein hotcombustion gases in each engine 24 a, 24 b cause rotation of a powerturbine coupled to an output shaft that is used to power the drivesystem coupled to the respective proprotor assemblies 20 a, 20 b. Thus,in this configuration, aircraft 10 is considered to be in a rotaryflight mode. FIG. 1B illustrates aircraft 10 in proprotor forward flightmode, in which proprotor assemblies 20 a, 20 b are rotating in asubstantially vertical plane to provide a forward thrust enabling wing14 to provide a lifting force responsive to forward airspeed, such thataircraft 10 flies much like a conventional propeller driven aircraft. Inthis configuration, engines 24 a, 24 b are operable in the turboshaftmode and aircraft 10 is considered to be in the rotary flight mode.

In the rotary flight mode of aircraft 10, proprotor assemblies 20 a, 20b rotate in opposite directions to provide torque balancing to aircraft10. For example, when viewed from the front of aircraft 10 in proprotorforward flight mode (FIG. 1B) or from the top in helicopter mode (FIG.1A), proprotor assembly 20 a rotates clockwise, as indicated by motionarrows 26 a, and proprotor assembly 20 b rotates counterclockwise, asindicated by motion arrows 26 b. In the illustrated embodiment,proprotor assemblies 20 a, 20 b each include three proprotor blades 22that are equally spaced apart circumferentially at approximately 120degree intervals. It should be understood by those having ordinary skillin the art, however, that the proprotor assemblies of the presentdisclosure could have proprotor blades with other designs and otherconfigurations including proprotor assemblies having four, five or moreproprotor blades. In addition, it should be appreciated that aircraft 10can be operated such that proprotor assemblies 20 a, 20 b areselectively positioned between proprotor forward flight mode andhelicopter mode, which can be referred to as a conversion flight mode.

A flight control computer 30 is schematically shown in fuselage 12, butit should be appreciated that flight control computer 30 may take anumber of forms and exist in a variety of locations within aircraft 10.Similarly, although flight control computer 30 is illustrated singly,flight control computer 30 can be illustrative of two, three, four orany other suitable number of flight control computers in aircraft 10,which computers can be located in same, similar or different locationswithin fuselage 12 or elsewhere in aircraft 10.

Flight control computer 30 is configured to control and communicate withvarious systems within aircraft 10 including, for example, local controlsystems 28 a and 28 b. Local control systems 28 a and 28 b areschematically shown in the proprotor assemblies 20 a and 20 b,respectively. The local control systems 28 a and 28 b can each becommunicably coupled to the flight control computer 30 and provideclosed-loop control of controllable elements located within theproprotor assemblies 20 a and 20 b. The controllable elements within theproprotor assemblies 20 a and 20 b can include any structural featureoperable to move and/or effect change such as, for example, blade locks,a gimbal lock, trailing-edge flaps, twistable blades, independentlycontrollable elements attached or connected to blades, combinations ofthe foregoing and/or the like.

The local control systems 28 a and 28 b can include, inter alia,actuators that control motion of the controllable elements in theproprotor assemblies 20 a and 20 b, sensors that provide feedback datarelated to the controllable elements and control computers that operatethe actuators, for example, by transmitting control signals to theactuators. Flight control computer 30 and the local control systems 28 aand 28 b can collaboratively provide a variety of redundant controlmethods relative to the controllable elements in the proprotorassemblies 20 a and 20 b.

FIG. 1C illustrates aircraft 10 in transition between proprotor forwardflight mode and airplane forward flight mode, in which engines 24 a, 24b have been disengaged from proprotor assemblies 20 a, 20 b andproprotor blades 22 of proprotor assemblies 20 a, 20 b have beenfeathered, or oriented to be streamlined in the direction of flight,such that proprotor blades 22 act as brakes to aerodynamically stop therotation of proprotor assemblies 20 a, 20 b. In this configuration,engines 24 a, 24 b are operable in turbofan mode wherein hot combustiongases in each engine 24 a, 24 b cause rotation of a power turbinecoupled to an output shaft that is used to power a turbofan that forcesbypass air through a fan duct to create forward thrust enabling wing 14to provide a lifting force responsive to forward airspeed, such thataircraft 10 flies much like a conventional jet aircraft. Thus, in thisconfiguration, aircraft 10 is considered to be in a non-rotary flightmode. FIG. 1D illustrates aircraft 10 in airplane forward flight mode,in which proprotor blades 22 of proprotor assemblies 20 a, 20 b havebeen folded to be oriented substantially parallel to respective pylonassemblies 18 a, 18 b to minimize the drag force generated by proprotorblades 22. In this configuration, engines 24 a, 24 b are operable in theturbofan mode and aircraft 10 is considered to be in the non-rotaryflight mode. The forward cruising speed of aircraft 10 can besignificantly higher in airplane forward flight mode versus proprotorforward flight mode as the forward airspeed induced proprotoraeroelastic instability is overcome.

Even though aircraft 10 has been described as having two engines fixedto the fuselage each operating one of the proprotor assemblies in therotary flight mode, it should be understood by those having ordinaryskill in the art that other engine arrangements are possible and areconsidered to be within the scope of the present disclosure including,for example, having a single engine that provides torque and rotationalenergy to both of the proprotor assemblies. In addition, even thoughproprotor assemblies 20 a, 20 b are illustrated in the context oftiltrotor aircraft 10, it should be understood by those having ordinaryskill in the art that the proprotor assemblies disclosed herein can beimplemented on other tiltrotor aircraft including, for example, quadtiltrotor aircraft having an additional wing member aft of wing 14,unmanned tiltrotor aircraft or other tiltrotor aircraft configurations.

Referring to FIGS. 2A-2G of the drawings, an exemplary mechanism fortransitioning a tiltrotor aircraft between rotary and non-rotary flightmodes is depicted and generally designated 100. In the illustratedembodiment, a rotor assembly 102 is depicted as a gimbal mounted, threebladed rotor assembly having a gimballing degree of freedom relative toa mast 104. Rotor assembly 102 includes a rotor hub 106 that is coupledto and operable to rotate with mast 104. Rotor hub 106 has a conicalreceptacle 108 extending from a lower portion thereof. Rotor hub 106includes three arms 110 each of which support a rotor blade assembly112, only one being visible in the figures. Each rotor blade assembly112 includes a cuff 114 and a rotor blade 116 that is pivotably coupledto cuff 114 by a connection member depicted as pin 118. As discussedherein, rotor blade assembly 112 has a pitching degree of freedom duringrotary flight and a folding degree of freedom during non-rotary flight.

The pitching and folding degrees of freedom of rotor blade assembly 112are realized using the highly reliable operation of swash plate 120.Swash plate 120 includes a non-rotating lower swash plate element 122and a rotating upper swash plate element 124. Swash plate element 124 isoperably coupled to each rotor blade assembly 112 at cuff 114 via apitch link 126 and a pitch horn 128, only one such connection beingvisible in the figures. A control system including swash plate actuators(not pictured) is coupled to swash plate element 122. The control systemoperates responsive to pilot input to raise, lower and tilt swash plateelement 122 and thus swash plate element 124 relative to mast 104. Thesemovements of swash plate 120 collectively and cyclically control thepitch of rotor blade assemblies 112 during rotary flight and fold rotorblade assemblies 112 during non-rotary flight.

Transitioning mechanism 100 includes a gimbal lock 130 that is coupledto and operable to rotate with mast 104. Gimbal lock 130 includes aconical ring 132, an actuation ring 134 and an actuator 136 including alift ring 138. Gimbal lock 130 is operable to selectively enable anddisable the gimballing degree of freedom of rotor assembly 102 relativeto mast 104. As best seen in FIG. 2A, gimbal lock 130 is disengaged fromrotor assembly 102, which enables the gimballing degree of freedom ofrotor assembly 102. In this configuration, there is an axial separationbetween conical ring 132 of gimbal lock 130 and conical receptacle 108of rotor hub 106 such that any teetering or flapping motion of rotorassembly 102 is not impacted by gimbal lock 130. When it is desired totransition the tiltrotor aircraft from the rotary flight mode and thenon-rotary flight mode, actuator 136 is operated to cause lift ring 138to raise actuation ring 134, which in turn raises conical ring 132 intoconical receptacle 108 of rotor hub 106. In this configuration, as bestseen in FIG. 2B, gimbal lock 130 is engaged with rotor assembly 102,which disables the gimballing degree of freedom of rotor assembly 102relative to mast 104 for non-rotary flight. In the illustratedembodiment, conical ring 132 has a conical geometry that is configuredto mate with a similar geometry of receptacle 108 thus disabling thegimballing degree of freedom of rotor assembly 102 relative to mast 104.It should be appreciated, however, that the exact mating geometry ofconical ring 132 and receptacle 108 is implementation specific and notlimited to the illustrated geometry.

Transitioning mechanism 100 also includes a blade stop assembly 140 thatis coupled to and operable to rotate with mast 104. Blade stop assembly140 includes three arms 142 that correspond to the three rotor bladeassemblies 112 of rotor assembly 102. In the illustrated embodiment,blade stop assembly 140 is integrated with gimbal lock 130 and sharesactuation ring 134, actuator 136 and lift ring 138 therewith, such thatoperation of blade stop assembly 140 occurs together with the operationof gimbal lock 130. It should be appreciated, however, that a blade stopassembly and a gimbal lock for use with the embodiments disclosed hereincould alternatively operate independent of one another. As best seen inFIG. 2A, arms 142 of blade stop assembly 140 have a radially contractedorientation, which provides clearance for rotor blade assemblies 112during rotary flight. When it is desired to transition the tiltrotoraircraft from the rotary flight mode and the non-rotary flight mode,actuator 136 is operated to cause lift ring 138 to raise actuation ring134, which in turn shifts arms 142 from the radially contractedorientation to a radially extended orientation, as best seen in FIG. 2B.In this configuration, arms 142 of blade stop assembly 140 will eachengage a cuff 114 of a rotor blade assembly 112 upon feathering therotor blade assemblies 112 responsive to lowering swash plate 120, asbest seen in FIG. 2C. In this manner, blade stop assembly 140 provides apositive stop for rotor blade assemblies 112.

Referring additionally to FIGS. 3A-3E, an exemplary transitioningmechanism 100 includes three blade lock assemblies 150, only one beingvisible in the figures. Each blade lock assembly 150 is selectivelyoperable to enable and disable the folding degree of freedom and thepitching degree of freedom of the respective rotor blade assembly 112.As illustrated, each blade lock assembly 150 includes a crank 152 thatis rotatably coupled to cuff 114 and rotatable with pitch horn 128 via aconnection member depicted as pin 154. In this manner, rotation of crank152 is responsive to the rise and fall of swash plate 120 in non-rotaryflight. Each blade lock assembly 150 also includes a link 156 that isrotatably coupled to rotor blade 116 at lug 158 via a connection memberdepicted as pin 160. Crank 152 and link 156 are coupled together at apivot joint 162. In the illustrated embodiment, coincident with pivotjoint 162, link 156 includes a pair of outwardly extending flanges 164each having a roller element 166 rotatably coupled thereto. Each flange164 is receivable in a seat 168 of cuff 114 when it is desired todisable the folding degree of freedom of rotor blade assembly 112.Preferably, an arch shaped geometry of the contact surface of each seat168 is sized such that a fully engaged flange 164 seated therein willhave two points of contact therewith providing a stiff connection,thereby minimizing any vibrations and/or relative movement between theparts.

Each blade lock assembly 150 further includes a blade lock 170 having afold lock position securing pivot joint 162 to cuff 114 and a pitch lockposition securing cuff 114 to arm 142 of blade stop assembly 140. Morespecifically, each blade lock 170 includes a fold lock 172 and a pitchlock 174. Each fold lock 172 consists of a pair of arms 176 that arerotatably coupled to respective seats 168 of cuff 114 via connectionmembers depicted as pins 178. Each arm 176 includes a wedge 180 having abearing surface that contacts a respective roller element 166 andprovides maximum contact force when fold lock 172 is fully engaged, asbest seen in FIG. 3A. Each pitch lock 174 includes a hasp 182 that isrotatably coupled to a pair of lugs 184 of cuff 114 via a connectionmember depicted as pin 186. Each hasp 182 includes a central openingoperable to selectively receive and retain a tab 188 of cuff 114 and atab 190 of arm 142 therein, as best seen in FIG. 3C. In the illustratedembodiment, fold lock 172 and a pitch lock 174 are coupled together by apair of adjustable connecting rods 192 such that a single actuator 194is operable to shift blade lock 170 between the fold lock position,depicted in FIG. 3A, and the pitch lock position, depicted in FIG. 3C.It should be appreciated, however, that a fold lock and a pitch lock foruse with the embodiments disclosed herein could alternatively operateindependent of one another.

The operation of transitioning mechanism 100 will now be described withreference to an exemplary flight of tiltrotor aircraft 10. For verticaltakeoff and hovering in helicopter flight mode, as best seen in FIG. 1A,and low speed forward flight in proprotor forward flight mode, as bestseen in FIG. 1B, tiltrotor aircraft 10 is in rotary flight mode. Toachieve this operational mode, engines 24 a, 24 b are in turboshaft modeto provide torque and rotational energy to proprotor assemblies 20 a, 20b, gimbal lock 130 is in the disengaged position enabling the gimballingdegree of freedom of rotor assemblies 102, as best seen in FIG. 2A, arms142 of blade stop assembly 140 are in the radially contractedorientation providing clearance for rotor assemblies 102, as best seenin FIG. 2A, and each of the blade lock assemblies 150 is enabling thepitching degree of freedom and disabling the folding degree of freedomof rotor blade assemblies 112, as best seen in FIG. 3A. In thisconfiguration, swash plate 120 collectively and cyclically controls thepitch of rotor blade assemblies 112 responsive to pilot input.

When it is desired to transition tiltrotor aircraft 10 from low speedforward flight in proprotor forward flight mode, as best seen in FIG.1B, to high speed forward flight in airplane forward flight mode, asbest seen in FIG. 1D, transitioning mechanism 100 is used to safelyachieve this result. As a preliminary step, engines 24 a, 24 b aretransitioned from turboshaft mode to turbofan mode until forward thrustis solely generated by engines 24 a, 24 b and tiltrotor aircraft 10 isin non-rotary flight mode. Swash plate 120 is now used to collectivelyshift the pitch of rotor blade assemblies 112 to the featheringposition, as best seen in FIG. 1C, wherein rotor blades 116 act asbrakes to aerodynamically stop the rotation of rotor assemblies 102. Todisable the gimballing degree of freedom of rotor assembly 102, actuator136 is operated to cause lift ring 138 to raise actuation ring 134,which in turn raises conical ring 132 into conical receptacle 108 ofrotor hub 106, as best seen in FIG. 2B. At the same time, responsive tolift ring 138 raising actuation ring 134, arms 142 shift from theradially contracted orientation to the radially extended orientation, asbest seen in FIG. 2B, to provide a positive stop for rotor bladeassemblies 112.

Next, actuators 194 are operated to shift blade locks 170 from the foldlock position, depicted in FIG. 3A, to the pitch lock position, depictedin FIG. 3C. Actuator 194 simultaneously causes hasp 182 to rotaterelative to lugs 184 of cuff 114 about pin 186 and arms 176 to rotaterelative to seats 168 of cuff 114 about pins 178, as best seen in FIG.3B. At the end of travel, hasp 182 has received tab 188 of cuff 114 andtab 190 of arm 142 in a central opening, as best seen in FIG. 3C, whichdisables the pitching degree of freedom of rotor blade assemblies 112.Also, at the end of travel, wedges 180 have cleared the lower portion ofseats 168, which enables the folding degree of freedom of rotor bladeassemblies 112. Swash plate 120 is now used to collectively shift rotorblade assemblies 112 from the radially outwardly extending featheringposition, as best seen in FIG. 1C, to a folded orientation, as best seenin FIGS. 1D and 2G.

With the pitching degree of freedom disabled, rise and fall of swashplate 120 now rotates pitch horn 128 relative to cuff 114, which in turncauses rotation of crank 152. The rotation of crank 152 causes rotationof link 156 relative to lug 158 about pin 160, rotation in pivot joint162, which disengages flanges 164 from seats 168, and rotation of rotorblade 116 relative to cuff 114 about pin 118, as best seen in FIGS. 2Fand 3D. Continued operation of swash plate 120 causes continued rotationof pitch horn 128, crank 152, link 156 and rotor blade 116 until rotorblade 116 reaches its desired folded orientation, as best seen in FIGS.2G and 3E. Tiltrotor aircraft 10 is now in airplane flight mode, whichis the high speed forward flight mode of tiltrotor aircraft 10 and is anon-rotary flight mode. In this operational mode, engines 24 a, 24 b arein turbofan mode providing no torque and rotational energy to proprotorassemblies 20 a, 20 b, gimbal lock 130 is in the engaged positiondisabling the gimballing degree of freedom of rotor assemblies 102, arms142 of blade stop assembly 140 are in the radially extended orientationproviding a position stop and coupling for rotor blade assemblies 112,and each of the blade lock assemblies 150 is disabling the pitchingdegree of freedom and enabling the folding degree of freedom of rotorblade assemblies 112.

When it is desired to transition back to proprotor forward flight mode,as best seen in FIG. 1B, from airplane forward flight mode, as best seenin FIG. 1D, transitioning mechanism 100 is used to safely achieve thisresult. With the pitching degree of freedom disabled, lowering swashplate 120 rotates pitch horn 128 relative to cuff 114, which in turncauses rotation of crank 152, link 156 and the unfolding of rotor blade116, as best seen in FIGS. 2F and 3D. Continued operation of swash plate120 causes continued rotation of pitch horn 128, crank 152, link 156 androtor blade 116 until rotor blade 116 reaches its desired radiallyoutwardly extending orientation, as best seen in FIG. 2E. In thisposition, crank 152 and link 156 are generally aligned such that flanges164 have entered seats 168, as best seen in FIG. 3C.

Next, actuators 194 are operated to shift blade locks 170 from the pitchlock position, depicted in FIG. 3C, to the fold lock position, depictedin FIGS. 2D and 3A. Actuator 194 simultaneously causes hasp 182 torotate relative to lugs 184 of cuff 114 about pin 186 and arms 176 torotate relative to seats 168 of cuff 114 about pins 178, as best seen inFIGS. 2D and 3B. At the end of travel, hasp 182 is remote from tab 188of cuff 114 and tab 190 of arm 142, as best seen in FIG. 3A, whichenables the pitching degree of freedom of rotor blade assemblies 112.Also, at the end of travel, wedges 180 have contacted roller element 166seating flanges 164 tightly within seats 168 and disabling the foldingdegree of freedom of rotor blade assembly 112, as best seen in FIG. 3A.Swash plate 120 may now be used to collectively shift rotor bladeassemblies 112 from the feathering position, as best seen in FIG. 1C, toa windmilling orientation.

To enable the gimballing degree of freedom of rotor assembly 102,actuator 136 is operated to cause lift ring 138 to lower actuation ring134, which in turn lowers conical ring 132 out of engagement withconical receptacle 108 of rotor hub 106, as best seen in FIG. 2A. At thesame time, responsive to lift ring 138 lower actuation ring 134, arms142 shift from the radially extended orientation to the radiallycontracted orientation, as best seen in FIG. 2A, to provide clearancefor rotor blade assemblies 112. Next, engines 24 a, 24 b aretransitioned from turbofan mode to turboshaft mode such that forwardthrust is provided by proprotor assemblies 20 a, 20 b and tiltrotoraircraft 10 is in the rotary flight mode. From this configuration,tiltrotor aircraft 10 may now be transitioned to helicopter mode when itis desired to hover and/or land the aircraft.

Operation of an exemplary over-centering blade lock 170 is describedwith additional reference to FIGS. 4-7 . Blade lock assembly 150includes an over-centering blade lock 170 having a fold lock positionsecuring pivot joint 162 to cuff 114 and a pitch lock position securingcuff 114 to arm 142 of blade stop assembly 140 (FIG. 2C). Eachover-centering blade lock 170 includes a fold lock 172 and a pitch lock174. Each fold lock 172 consists of a pair of arms 176, e.g. levers,that are rotatably coupled to respective seats 168 of cuff 114 viaconnection members depicted as pins 178. In some embodiments, each arm176 includes a wedge 180 having a bearing surface that contacts arespective roller element 166 and provides maximum contact force on link156 when fold lock 172 is fully engaged, as best seen in FIG. 3A. Themaximum contact force may correspond to center position 400 ofover-centering blade lock 170. Each pitch lock 174 includes a hasp 182that is rotatably coupled to a pair of lugs 184 of cuff 114 via aconnection member depicted as pin 186. Each hasp 182 includes a centralopening operable to selectively receive and retain a tab 188 of cuff 114and a tab 190 of arm 142 therein, as best seen in FIGS. 3C and 6 . Inthe illustrated embodiment, fold lock 172 and a pitch lock 174 arecoupled together by a pair of adjustable connecting rods or fold links192 such that a single actuator 194 is operable to shift over-centeringblade lock 170 between the fold lock position, depicted in FIGS. 4 and 5, and the pitch lock position, depicted in FIG. 6 .

Over-centering blade lock 170 uses geometry and spring force tomechanically secure fold lock 172 in the blade fold lock position forrotary flight. In a traditional blade lock assembly, an electric motor,such as actuator 194, provides continuous pressure on hasp 182 and foldlink 192 to maintain arm 176 in the fold lock position. Over-centeringblade lock 170 provides a passive lock to maintain fold lock 172 in theblade fold lock position without requiring a secondary locking force.

Each fold link 192 is pivotally connected at a first end 191 to hasp 182at a position 183 and pivotally connected at a second end 193 to arm 176of fold lock 172 at position 175. Hasp 182 serves as bellcrank thatpivots about connection member 186. Axis 400 illustrates the centerposition of over-centering blade lock 170, extending through pivot point186 and pivot joint 162, and the position of fold link 192 when arm 176is in the fold lock position. When hasp 182 is rotated about connectionmember 186 to the position contacting hard stop 402, illustrated as lug184 secured to cuff 114, fold link 192 is located over-center position400.

In the fold lock position, fold link 192 and hasp 182 are longer than aresolved length of axis 400 so that fold link 192 is deflected orcompressed when rotated to the over- center position. As illustrated inFIG. 5 , axis 400 has a resolve length (L3) extending from pivotconnection 186 (bellcrank axis) of hasp 182 to the pivot connection 193of link 192 to arm 176. Hasp 182 has a radius or length (L1) from hasppivot connection 186 to first end pivot connection 191 of link 192 tohasp 182. Fold link 192 has a length (L2) from first end pivotconnection 191 to second end pivot connection 193 at arm 176. Thus, inthe fold locked position the length (L1) of hasp 182 plus the length(L2) of link 192 is greater than the resolved distance (L3) frombellcrank axis 186 to pivot connection 193 of fold link 192 to arm 176.The deflected or compressed fold link 192 provides a spring forceholding arm 176 in the locked position and resisting a counter-forceurging arm 176 to an unlocked position. In this over-center position,link 192 and hasp 182 resist a counter-force that pushes on arm 176 andresists backdriving blade lock 170 out of the blade fold lock positionof FIG. 4 . The amount of over-center interference is the limit ofdeflection of over-centering blade lock 170 before arm 176 is allowed tomove out of the locked position. Thus, if the over-centering blade lock170 system deflects or compresses more than the over-center interferencearm 176 can move out of the lock position or at least arm 176 will notbe wedged with link 156 with sufficient force to prevent folding orpartial folding of the proprotor blade. For example, if the combinationof hasp 182 (L1) and fold link 192 (L2) are 0.1 inches longer thanresolved distance of axis 400, then the blade lock system can deflect orcompress approximately 0.1 inches before unlocking.

FIG. 6 shows fold link 192 in a below-center position with blade lock170 out of the blade fold lock position enabling the folding degree offreedom of the rotor blade assembly and hasp 182 in the pitch lockposition disabling the pitching degree of freedom of the rotor bladeassembly.

FIG. 7 illustrates an exemplary adjustable hard stop mechanism generallydesignated with the numeral 410. With additional reference to FIGS. 4-6, adjustable hard stop mechanism 410 provides a means to adjust theover-center location of fold link 192 relative to center position 400when hasp 182 contacts hard stop 402 and sets the preload of the systemin the locked position. The preload identifies the force required tomove fold link 192 from the over-center position to unlock fold lock172. The preload force is the force applied by arm 176 to link 176 toprevent link 156 and thus the proprotor blade from folding. Adjustablehard stop mechanism 410 includes a set screw 404 threadedly connected toone of hasp 182 or cuff 114, for example lug 184. In the example of FIG.7 , set screw 404 is threadedly connected to hasp 182 such that thelength of set screw 404 extending from hasp 182 can be varied.

Conditional language used herein, such as, among others, “can,” “might,”“may,” “e.g.,” and the like, unless specifically stated otherwise, orotherwise understood within the context as used, is generally intendedto convey that certain embodiments include, while other embodiments donot include, certain features, elements and/or states. Thus, suchconditional language is not generally intended to imply that features,elements and/or states are in any way required for one or moreembodiments or that one or more embodiments necessarily include suchelements or features.

The term “substantially,” “approximately,” and “about” is defined aslargely but not necessarily wholly what is specified (and includes whatis specified; e.g., substantially 90 degrees includes 90 degrees andsubstantially parallel includes parallel), as understood by a person ofordinary skill in the art. The extent to which the description may varywill depend on how great a change can be instituted and still have aperson of ordinary skill in the art recognized the modified feature asstill having the required characteristics and capabilities of theunmodified feature. In general, but subject to the preceding, anumerical value herein that is modified by a word of approximation suchas “substantially,” “approximately,” and “about” may vary from thestated value, for example, by 0.1, 0.5, 1, 2, 3, 4, 5, 10, or 15percent.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the disclosure.Those skilled in the art should appreciate that they may readily use thedisclosure as a basis for designing or modifying other processes andstructures for carrying out the same purposes and/or achieving the sameadvantages of the embodiments introduced herein. Those skilled in theart should also realize that such equivalent constructions do not departfrom the spirit and scope of the disclosure and that they may makevarious changes, substitutions, and alterations without departing fromthe spirit and scope of the disclosure. The scope of the inventionshould be determined only by the language of the claims that follow. Theterm “comprising” within the claims is intended to mean “including atleast” such that the recited listing of elements in a claim are an opengroup. The terms “a,” “an” and other singular terms are intended toinclude the plural forms thereof unless specifically excluded.

What is claimed is:
 1. A blade lock for a tiltrotor aircraft to enableand disable a folding degree of freedom and a pitching degree of freedomof a rotor blade assembly, the blade lock comprising: a crank and ablade link coupled at a crank pivot point, the blade link rotatablycoupled to a rotor blade and the crank rotatably coupled to a cuff ofthe rotor blade assembly and operable to rotate relative to the cuff; alever pivotally connected to the cuff at a lever pivot point and havinga fold locked position securing a crank pivot joint to the cuffdisabling the folding degree of freedom and a fold unlocked positionenabling the folding degree of freedom; a bellcrank pivotally connectedto the cuff at a bellcrank pivot point; a center position extendingthrough the bellcrank pivot point and the crank pivot point; a fold linkhaving an end pivotally connected to the lever at a link-leverconnection and an opposite end pivotally connected to the bellcrank at alink-bellcrank connection; and a projection extending from the bellcrankat a location between the bellcrank pivot point and the link-bellcrankconnection; wherein the lever is unsecured in the fold locked positionwhen the fold link is in the center position and the projection is notin direct contact with the cuff; wherein the lever is secured in thefold locked position when the fold link is in an over-center positionand the projection is in direct contact with the cuff; and wherein thefold link is deflected or compressed in the center position when thefold link is rotated between the fold unlocked position and theover-center position.
 2. The blade lock of claim 1, comprising anactuator coupled to the bellcrank to rotate the fold link to the centerposition and to the over-center position.
 3. The blade lock of claim 1,wherein the bellcrank is a pitch lock configured to enable the pitchingdegree of freedom when the lever is in the fold locked position and todisable the pitching degree of freedom when the lever is moved out ofthe fold locked position.
 4. The blade lock of claim 1, wherein theprojection is a set screw.
 5. The blade lock of claim 1, wherein theprojection is moveable to change a distance that the projection extendsfrom the bellcrank.
 6. The blade lock of claim 1, wherein the projectionis threadedly connected to the bellcrank.
 7. The blade lock of claim 1,comprising an actuator coupled to the bellcrank to rotate the fold linkto the center position and to the over-center position; and theprojection is moveable to change a distance that the projection extendsfrom the bellcrank.
 8. The blade lock of claim 7, wherein the projectionis threadedly connected to the bellcrank.
 9. The blade lock of claim 7,wherein the bellcrank is a pitch lock configured to enable the pitchingdegree of freedom when the lever is in the fold locked position and todisable the pitching degree of freedom when the lever is moved out ofthe fold locked position.